The present invention refers to a chemoelectric cell containing a positive electrode and a negative electrode with electrolyte disposed in the interspace between the two electrodes, whereby at least one electrode is a gas electrode, with means for supply and discharge of an electrochemically active substance in the gaseous state.
Gas diffusion electrodes are used in many new electrochemical power sources, for instance metal air cells, methanol air cells, different types of fuel cells, etc. One side of the gas diffusion electrode is in contact with a gas phase (for instance the air space in a metal air cell or the hydrogen space in a hydrogen air cell) and the other side is exposed to an electrolyte phase which, in turn, is in contact with the other electrode in the actual chemoelectric cell (for instance the metal anode in a metal air cell).
Gas diffusion electrodes are used also in chemoelectric cells for electrolysis, for instance electrolytic cells for the production of chlorine and alkali. The present invention can also be used with such chemoelectric cells.
The nomenclature in this filed is not very clear. In this description "gas electrode" means a complete electrode for electrochemical reaction of the substance which is supplied in the gaseous state to the electrode. The active part of the gas electrode where the electrochemical reactions are taking place in simultaneous contact between the electrode material, the electrolyte, and the gas, is herein called "gas diffusion electrode." The gas diffusion electrode is, in general, porous and contains therefore most often a gas phase, an electrolyte phase, and the solid electrode material.
The gas electrodes according to the present state of art exhibit, as will be demonstrated in some detail below, quite difficult design problems when it comes to achieving sufficient mechanical stability and assuring supply of gas and electronic conduction. The gas electrodes therefore occupy a much larger volume than what is dictated by the electrocatalytic function which, in turn, requires but very small amounts of catalysts, which in general occupy a very small part of the volume of the gas electrode.
The present invention involves a completely new design of gas electrodes which permit a sizable reduction of the volume requirements of the gas electrode. A number of other advantages are also obtained, like greater simplicity and a more robust mechanical design, which is of great importance, for instance in tractionary applications. I shall, to begin with, describe the invention using a metal air battery as an example. I will also give examples of hydrogen air batteries and electrolytic cells according to the invention.
Comparison between an alkaline iron air cell and an alkaline iron nickel cell of conventional design shows that the positive nickel oxide electrode in the conventional alkaline accumulator corresponds to the air electrode, which in this case comprises two gas diffusion electrodes and the air space between them. One advantage with the iron air cell compared to the iron nickel cell is, of course, that any active material need not be stored in the air electrode, which is fed with the oxygen of the air, whereas the positive nickel oxide electrode must contain all the active positive material for the electrochemical processes. This active material represents important weight, volume, and costs factors at large capacities. Material usage, volume requirement, and weight for conventional air electrodes are, however, not negligible items as was indicated above. The cathode cost is frequently a dominating item in the material calculus for iron air cells.
It is an object of the present invention to eliminate or minimize problems of the herebefore encountered.
It is another object to provide a novel electrochemical cell.